The present invention relates to shredding and grinding systems and, more particularly, to shredding and grinding systems which incorporate multiple augers.
In order to reduce large, bulky items such as wood pallets, crates, 55 gallon drums of liquid or hardened material, railroad ties and the like, shredding machines have been developed which incorporate a single rotating auger to reduce and compress such waste material. An example of such a device is disclosed in Koenig U.S. Pat. No. 4,253,615. That patent shows an auger shredder having a frame which defines a grinding chamber, a tapered auger mounted within the grinding chamber and powered by a low-speed hydraulic motor, and a discharge extrusion tube which extends outwardly from the front wall of the grinding chamber and is concentric with a rotational axis of the auger. The auger includes a central shaft and a tapered flight having teeth projecting radially from the flight periphery. The teeth mesh with stationary breaker bars mounted on the bottom of the grinding chamber, which is concave and tapered to follow contour of the auger flight and guide material toward the discharge extrusion tube.
Material deposited in the grinding chamber is grabbed by the teeth and pulled downwardly where it is broken up by the meshing action of the teeth and breaker bars. The broken material is further shredded and compressed by the pumping action of the tapered flight, which forces the material forwardly to the extrusion tube. Once in the extrusion tube, which preferably is of a frusto-conical shape, the material is further compressed and shredded by the action of the leading edge of the flight upon the rear face of the material within the tube.
The material within the tube forms a plug which may act as barrier to prevent back flow of harmful gases or flames. This aspect of the design is particularly useful when the auger shredder feeds shredded material to an incinerator.
However, there exists a disadvantage with this type of grinding device in that the extrusion tube must be rectilinear in shape; that is, it cannot curve or angle away from the discharge opening since it is difficult to push the plug through an angled tube without creating jams. Consequently, such grinding devices must be elevated and otherwise oriented so that the discharge tube is substantially at the same level as the inlet to the receptacle and is aligned with the inlet of the receptacle. Furthermore, since these devices rely upon a gravity feed to force material into the grinding chamber, the grinding chamber must be held substantially horizontal. This often requires that the device be elevated on a support framework if the inlet to the incinerator or other receptacle is also elevated.
Another disadvantage with such devices is that, with a single auger, the compression ratio achievable by its auger--which is defined as the reduction in volume between successive flights from the large diameter end of the auger to the small diameter end--of greater than 6:1 are difficult to obtain and result in increased power requirements, reduced flow rate of material and build up of material on the front wall of the grinding chamber.
Accordingly, there is a need for an auger shredder system which can propel ground material from the grinding chamber to an inlet at a different elevation. There is also a need for an auger shredder system in which compression ratios of greater than 6:1 are achievable.